Field of the Invention
The present invention relates to a heat treatment apparatus that irradiates a thin-plate precision electronic substrate (hereinafter, merely referred to as a “substrate”) such as a semiconductor wafer with flash light to heat the substrate and relates to a method for manufacturing the heat treatment apparatus.
Description of Background Art
In the manufacturing process of a semiconductor device, the introduction of impurities is an essential step for forming pn junctions in a semiconductor wafer. Currently, impurities are typically introduced by ion implantation and subsequent annealing. Ion implantation is a technique for physically implanting impurities by ionizing impurity elements such as boron (B), arsenic (As), and phosphorus (P) and causing the impurity elements to collide with a semiconductor wafer at a high acceleration voltage. The implanted impurities are activated by annealing. If, at this time, annealing time is approximately several seconds or more, the implanted impurities are deeply diffused by heat. As a result, a junction depth may become deeper than necessary, possibly interfering with excellent formation of a device.
Thus, flash lamp annealing (FLA) has recently been receiving attention as an annealing technique for heating a semiconductor wafer in an extremely short time. The flash lamp annealing is a heat treatment technique for raising the temperature of only a surface of the semiconductor wafer implanted with impurities in an extremely short time (a few milliseconds or less) by irradiating the surface of the semiconductor wafer with flash light using xenon flash lamps (hereinafter, the term “flash lamps” used means xenon flash lamps).
The xenon flash lamps have a spectral distribution of radiation ranging from ultraviolet regions to near-infrared regions. A wavelength of light emitted from the xenon flash lamps is shorter than that of light emitted from conventional halogen lamps and substantially coincides with a fundamental absorption band of a silicon semiconductor wafer. Thus, the temperature of the semiconductor wafer can be rapidly increased with a small amount of transmitted light when the semiconductor wafer is irradiated with flash light from the xenon flash lamps. It has been determined that the irradiation with flash light in an extremely short time of a few milliseconds or less can selectively raise the temperature of only near the surface of the semiconductor wafer. Accordingly, such a temperature rise in an extremely short time using the xenon flash lamps allows impurities to be only activated without being deeply diffused.
In a lamp annealing apparatus including the flash lamps, an O ring is used as a sealing member for making a chamber airtight, the chamber housing the semiconductor wafer. The O ring is made of resin and has a relatively low heat resistance, so that measures to suppress a temperature rise (for example, cooling of the chamber by exploiting cooling fluid) are needed when the O ring is used in a heat treatment apparatus. Particularly in a case where the O ring is used in the heat treatment apparatus including the flash lamps, extremely intense flash light is instantaneously emitted, thereby resulting in degradation of a surface of the O ring due to the irradiation with the intense flash light rather than degradation of the O ring due to heat. The degradation of the surface of the O ring not only causes a loss of airtightness in the chamber but also generation of gas and particles, thereby leading to the serious problems.
For this reason, Japanese Patent Application Laid-Open No. 2009-4427 proposes that a rough surface diffusely reflecting light is formed on a back surface of a clamping ring by sand blasting in an apparatus in which an O ring is sandwiched between a chamber side wall and a quartz window and seals them together by pressing the quartz window against the chamber with the clamping ring. Even if part of flash light travels into the portion between the clamping ring and the chamber side wall during irradiation with the flash light, the light is diffusely reflected by the rough surface on the back surface of the clamping ring. This prevents the light from reaching the O ring, which can prevent the degradation of the O ring.
Flash-lamp annealing apparatus for activating impurities as disclosed in Japanese Patent Application Laid-Open No. 2009-4427 has been used in normal pressure. However, application of flash lamp annealing to different treatment purposes (for example, heat treatment of a high dielectric gate insulating film) has been taken into consideration, and pressure in the chamber may be reduced to a vacuum according to a treatment purpose in some cases. To reduce the pressure in the chamber to a vacuum, the chamber itself needs to have a pressure-resistant structure, and a quartz window that closes the opening of the chamber needs to have a thickness greater than that disclosed in Japanese Patent Application Laid-Open No. 2009-4427.
However, it has been determined that the quartz window having the greater thickness causes an increased amount of flash light traveling into the quartz window during irradiation with flash light and that the degradation of the surface of the O ring cannot be sufficiently prevented by only blasting the back surface of clamping ring because the O ring is exposed to the flash light.